in 68/69 I worked until 10:00 every night I wanted to while in high school. That was in Cincinnati.
These laws changed drastically in the 70s. Especially in Southern states such as AL. That's when they banned people under 18 from working in manufacturing, industrial and farming positions involving machinery, and limited their hours in other jobs if they were going to school.
Even on weekends, kids could work no more than 6-8 hrs a shift and had to be given a 30-minute lunch.